1. Field of the Invention
This invention relates generally to the field of lasers, and more particularly to lasers having multiple elements of lasing medium and a folded beam path.
2. Description of the Background Art
Known solid state lasers include a crystal of active laser medium, for example a cylindrical rod of ruby or neodimium-doped yttrium aluminum garnet (YAG), and one or more pumping lamps, enclosed in a highly reflective housing. A highly reflecting mirror and a partially reflecting mirror are positioned to face one another at opposite ends of the laser medium such that light emitted from the laser medium is reflected back and fourth between the highly and partially reflecting mirrors.
The pumping lamps produce light which excites the atoms of the laser medium to a metastable state. The relaxation of the excited atoms to their ground state is accompanied by the emission of light. Some of the emitted light is reflected back and fourth between the end mirrors, and the growing reflected wave induces the emission of additional light into the reflected wave state. The partially reflecting mirror, also referred to as an output coupler, allows a portion of the reflected light to pass as the output beam of the laser.
The power output of solid state lasers depends upon, among other things, the length of the path of the beam within the laser medium. Thus, the power output of such a laser can be increased by increasing the length of the laser medium. This approach has at least two practical limitations, however. First, rods of increased length are difficult and expensive to manufacture. Second, beam quality deteriorates rapidly when rods exceed six to eight inches in length.
Due to the limitations of a single long rod, typical high powered lasers employ multiple short rods. FIG. 1 shows a cross-sectional view of a prior art multirod laser 100. Prior art laser 100 includes pump chambers 102(1-3), high reflector 108 which has a highly reflecting face 109, and output coupler 110 which has a partially reflecting face 111.
Pump chambers 102(1-3) include cylindrical laser rods 112(1-3) and two cylindrical arc lamps 114(1-3) and 116(1-3), mounted axially parallel in highly reflecting housings 118(1-3). Pump chambers 102(1-3) are aligned such that the axes of laser rods 112(1-3) are colinear and define an optical path 130 which is perpendicular to faces 109 and 111 of high reflector 108 and output coupler 110, respectively.
Combining multiple pump chambers in series as shown in laser 100 significantly increases output power, but the number of pump chambers that can be used in a system is practically limited by increased length making the system more awkward to work with and requiring more complex alignment processes to optimize the laser output.
Prior art patents have suggested folding the optical path of a laser to decrease the laser length overall and increase the optical path length within the active laser medium. For example, U.S. Pat. No. 5,148,443, issued to Du et al. teaches folding the beam within a single cavity of active laser medium by providing retroreflecting mirrors at each end of the cavity. This approach appears well-suited to gas lasers, but if the laser medium is solid state, then the size of the cavity is limited to the size of the available medium crystal. Thus, as applied to solid state lasers, Du et al. suffers the same limitations as the single crystal lasers described above.
Similarly, U.S. Pat. No. 3,361,987, issued to DeMaria, teaches folding the beam within a single poly-sided crystal. This single crystal method suffers the same limitations as do the single crystal lasers described above.